The present invention relates to a tire loader for loading a green tire into a vulcanizing press.
As disclosed Japanese Patent Publications Nos. 46-22099, 46-38330, 50-31911, and 46-24773, one known type of tire loader includes a plurality of grippers interlinked by a link mechanism and openable and closable by a force applied vertically along a central axis against interconnected portions of the grippers. Another conventional tire loader has a movable disk having cam grooves for opening and closing grippers, as shown in Japanese Patent Publication No. 52-991.
The former tire loader construction is disadvantageous in that since the drive source such as a pneumatic cylinder is disposed in an axial direction, the grippers have an increased height, and it is necessary to provide a large space between upper and lower dies when they are opened. This causes a serious problem with a vertically movable press recently available to achieve an increased degree of accuracy. Specifically, the up-and-down stroke of the press needs to be increased by an increased height of the grippers which enter between the upper and lower dies, so that it takes a longer period of time for the press to be opened and closed and the overall press height becomes larger. Therefore, green tires cannot be pressed economically.
Another difficulty is that since the grippers depend from the swinging links, the grippers cannot be circularly arranged precisely due to errors in accuracy of the individual links and backlash in the swinging ends of the links.
The latter tire loader type also has various shortcomings. It is difficult to arrange the grippers circularly accurately as a number of complex cam grooves cannot be formed accurately in the cam disk. The cam disk is large in size and weight.
In addition, both tire loader types have the following common defects:
The grippers in the loaders are required to grip unvalcanized green tires with as small a force as possible. With the prior tire loaders, the movement of the grippers is limited by either limiting the movement of the drive source or providing the grippers respectively with stops for limiting their movement. The individual stops, six to eight stops, for example, on the grippers need to be adjusted each time a tire to be gripped has a different size. Since such frequent gripper adjustment is not preferred by the user, radial positions of the grippers are normally limited through limiting the movement of the drive source in most applications. With the link mechanism, however, the ratio of the movement of the drive source to the movement of the gripper varies with the radial gripper position. This requires extreme care and a long period of time to achieve a proper gripping diameter.
The conventional tire loader operates such that the lower bead of a green tire is seated on the lower bead ring of a lower die while the upper bead of the tire is gripped. With such a lower-bead-set-first system, as shown in FIG. 1, the green tire T is positionally unstable and is supported by a bladder 01 inflated at an extremely low temperature. The green tire T tends to be tilted with respect to the central axis due to a slight irregularity of the bladder 01. The tire is sometimes likely to be seated erroneously on an upper bead ring 02. Such a problem can be solved by seating the tire on the lower bead ring 03, then on the upper bead ring 02, and finally by inflating the bladder 01. However, the tire would tend to collapse since the tire has side walls 04 of reduced rigidity and most of the weight concentrates on treads 05.
In the tire loader of the foregoing lower-bead-set-first arrangement, the upper bead of the green tire placed on a green tire mount disposed outside of the press is gripped from inside by expansible and contractible grippers lowered from above the green tire, or the treads of the green tire are gripped from outside. In any case, the green tire mount is needed in front of the press. Various dies are replaceably mounted in the press to provide a capability to vulcanize many kinds of tires. The green tire mount should be movable in order not to interfere with die replacement. The green tire mount should have adjustable tire holders for holding green tires of different sizes. Therefore, the known green tire mount has been expensive, resulting in an increase in the cost of the tire loaders.
To eliminate the difficulties with the conventional lower-bead-set-first tire loaders, the applicant has proposed a tire loader of the upper-bead-set-first type for seating the upper bead of a green tire on the upper bead ring of an upper die, seating the lower bead of the green tire on the lower bead ring of a lower die, and inflating a bladder in the green tire thus supported by the upper and lower bead rings to shape the green tire. The loader of such a construction has extensible and contractible grippers opening upwardly and mounted on a loader arm movable upwardly and downwardly and angularly movable horizontally. When the grippers grip the green tire to load the latter into the press, the grippers are required to be opened upwardly. If the grippers were open upwardly at the time the green tire is supplied in a first position outside of the press, then the following problems would arise: Since large-size tires have increased outside diameters and are heavy (about 100 Kg), they could not be manually brought onto the grippers remaining open upwardly. It would then be necessary to provide a complex and costly mechanical tire transfer device in front of the press or on a green tire supply carriage. This would increase the cost of the tire loader. The tire loader also has suffered the danger of allowing a green tire to collapse and be deformed under its own weight while the tire loader is holding the tire prior to vulcanization thereof. There is a need for some preventive measure to avoid such a problem.